Polyols of tetrahydropyrimidines

ABSTRACT

Methylol derivatives of 2,3,4,5-tetrahydropyrimidines and to uses thereof, particularly as corrosion inhibitors.

In U.S. Pat. No. 4,145,545 there is described and claimed a method ofpreparing Substituted 2,3,4,5-tetrahydropyrimidines (THP) of the formula##STR1## where R₁, R₂, R₃, R₄, R₅ and R₆, which may be the same ordifferent, are hydrogen or substituted group such as alkyl, aryl,cycloalkyl, alkaryl, aralkyl, heterocyclic, substituted derivativesthereof, etc. In addition, the R groups may be joined in a cyclicconfiguration which makes the THP structure a part of the substitutedgroup.

Alkyl includes methyl, ethyl, propyl, butyl, amyl, hexyl, heptyl, octyl,nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,hexadecyl, heptadecyl, octadecyl, escosyl, docosyl, etc. for examplehaving about 1-25 or more carbons such as from about 1-18 carbons, butpreferably about 1-12 carbons. The term "alkyl" also includes isomers ofthe straight chain where branching occurs.

Cycloalkyl includes cyclopentyl, cyclohexyl, etc. and derivativesthereof such as alkyl cyclohexyl, dialkylcyclohexyl, etc.

Aryl, alkaryl and aralkyl include phenyl, alkylphenyl, polyalkylphenyl,chlorophenyl, alkoxyphenyl, naphthyl, alkylnaphthyl, etc., benzyl,substituted benzyl, etc.

The joining of the R groups into a ring structure include thosestructures derived from reactants of the general formula ##STR2## suchas cyclohexanone, cyclopentanone, substituted derivatives thereof suchas alkyl-cyclohexanone, dialkyl-cyclohexanone, etc.

We have now discovered that the THP's prepared in U.S. Pat. No.4,145,545 can be reacted with an aldehyde such as formaldehyde to yieldmethylol derivatives of THP.

The reaction is carried out by reacting the THP with formaldehyde underconditions which produce the desired product. In practice aqueousformaldehyde (formalin) is employed. The reaction is carried out atabout room temperature or higher, such as from about 25° to 140° C., forexample from about 25° to 70° C., but preferably from about 25° to 40°C.

The stoichiometric ratio of THP to formaldehyde can vary widely fromabout 1 to 6, such as from about 1 to 5, but preferably from about 1 to4.

In general, one employs at least one mole equivalent of formaldehyde foreach mole equivalent one desires to be present in the derivative. Thus,if one desires the derivative to have 1 methylol group the ratio offormaldehyde to THP is at least 1; two methylol groups, the ratio is atleast 2; three methylol groups the ratio is at least 3; 4 methylolgroups the ratio is at least 4, etc. At ratios of less than 4/1, a largevariety of methylol derivatives are obtained. The most favored reactionsites being the 3 position (i.e. N-H) and the methyl group (CH₃) at the6 position.

The following Table A presents typical examples of THP's prepared inU.S. Pat. No. 4,145,545 which can be reacted in accord with the presentinvention:

                  TABLE A                                                         ______________________________________                                         ##STR3##                                                                     Ring Position                                                                 6        5     4        4    2        2                                       Subst. Group                                                                  Ex.  R.sub.1 R.sub.2                                                                             R.sub.3                                                                              R.sub.4                                                                            R.sub.5  R.sub.6                               ______________________________________                                        1    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           CH.sub.3 CH.sub.3                              2    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        CH.sub.3                              3    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        n-C.sub.3 H.sub.7                     4    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        n-C.sub.6 H.sub.13                    5    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        i-C.sub.5 H.sub.11                    6    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        Phenyl                                7    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        i-C.sub.7 H.sub. 15                   8    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        n-C.sub.8 H.sub.17                    9    CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        CH.sub.3                              10   CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        CH.sub.3                              11   CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           H        C.sub.2 H.sub.5                       12   CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           (CH.sub.2).sub.5                               13   CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                            ##STR4##                                      14   CH.sub.3                                                                              H     CH.sub.3                                                                             CH.sub.3                                                                           (CH.sub.2).sub.5                               ______________________________________                                    

In the present process, it is preferred that R₂ be hydrogen so thatsubstitution can occur at this position. Large R groups in the 2position (i.e. R₅ and R₆) such as those having 3 or more carbons forexample ##STR5## tend to impede substitution in the 3-position (i.e.NH).

The following equation illustrates the reactions of the presentinvention: ##STR6## In the above equation n=4.

Specific illustrations include the following:

    ______________________________________                                        I a-e               II a-e                                                    R.sub.1       R.sub.2   R.sub.1     R.sub.2                                   ______________________________________                                        a     H           H         H         H                                              ##STR7##   H                                                                                        ##STR8## H                                       c     CH.sub.3 CH.sub.2 CH.sub.2                                                                H         CH.sub.3 CH.sub.2 CH.sub.2                                                              H                                       d                                                                                    ##STR9##   H                                                                                        ##STR10##                                                                              H                                       e     R.sub.1 + R.sub.2 = (CH.sub.2).sub.5                                                            R.sub.1 + R.sub.2 = (CH.sub.2).sub.5                  ______________________________________                                    

Reaction where n is less than 4 produces mixtures with the --CH₂ OHgroup located at one or more of the four possible reaction sites 3, 5,and 6 (one or two CH₂ OH's on the methyl group). Large R-substituents atposition 2 usually hinder reaction at the 3 position (--NH).

The following examples are presented for purposes of illustration andnot of limitation.

EXAMPLE 1 4,4,6-Trimethyl 2,3,4,5-tetrahydropyrimidines

In a 2 liter three necked round-bottom flask equipped with a mechanicalstirrer, a thermometer, and a reflux condenser was charged a mixture of196.3 g of mesityl oxide and 400 ml. of concentrated ammonium hydroxide.The mixture was stirred at room temperature for 18 hours. To thismixture was added 162.3 g of 37% formaldehyde (in H₂ O) over 20 minutes.An ice-water bath was used to maintain the reaction temperature at 40°.This mixture was stirred at room temperature for 18 hrs. The excessammonia was removed by distillation under reduced pressure. Theremaining liquid was distilled to yield 176.7 g (68.5% of theory) of4,4,6-trimethyl-2,3,4,5-tetrahydropyrimidine. ¹³ C NMR (solvent CDCl₃),δ in ppm, internal standard t.m.s.

    ______________________________________                                        a. b. c. d. e. f. g.                                                                  61.29 27.66 45.91 27.66 42.14 27.66 164.73                                             ##STR11##                                                    ______________________________________                                    

% N Calc 22.22; Found 19.36.

In a similar manner products were made where ##STR12##

EXAMPLE 2

Reaction of product from example 1 (R═H, Ia) with formaldehyde. In a 200ml three-necked flask equipped with a mechanical stirrer, a thermometer,and a reflux condenser was charged 20 g Ia and 51.4 g of 37%formaldehyde solution. The mixture was stirred at room temperature for 5hrs. The solvent was removed by distillation under reduced pressure, toyield 33.2 g of a very viscous liquid (84.6% of theory). ¹³ C NMR(solvent CDCl₃), δ in ppm, internal standard t.m.s.

    ______________________________________                                         ##STR13##          a. 69.99 b. 80.97 c. 22.92 d. 51.17 e.                                                  f. g. h. i. j.                                                                      49.28 62.98 172.06 43.70 61.29            ______________________________________                                    

% N:Calc. 11.38; Found 11.85.

The product is a result of 4 moles formaldehyde reacting with thetetrahydropyrimidine.

EXAMPLE 3

In a similar manner to that in example 2, tetrahydropyrimidine, Ia (20g) was reacted with 38.6 g of 37% formaldehyde (1/3 molar ratio) 36.2 gof viscous liquid was obtained (87.7% of theory). A mixture of productsare possible containing three methylol groups. ##STR14##

¹³ C NMR data favors structure A as the major product.

% N:Calc. 12.96; Found 14.09.

EXAMPLE 4

In a similar manner to that in example 2, tetrahydropyrimidine Ia (20 g)was reacted with 25.9 g of 37% formaldehyde (1/2 molar ratio). 25.3 ofviscous liquid product (85.4% of theory) was obtained. Again a mixtureof products are possible.

% N:Calc. 15.05; Found 16.06. ##STR15##

EXAMPLE 5

In a similar manner to example 2, tetrahydropyrimidine, Ia (20 g) wasreacted with 13 g of 37% formaldehyde (1/1 molar ratio). 20.8 g ofviscous liquid product (83.9% of theory) was obtained. Possible productsare: ##STR16##

% N Calc. 17.45; Found 18.91.

EXAMPLE 6

In a similar manner to example 2, tetrahydropyrimidine Ib ##STR17##(33.6 g) was reacted with 64.9 g of 37% formaldehyde (1/4 molar ratio).50.4 g (87.5% of theory) of viscous product was obtained.

% N:Found 9.70; % N:Calc. 3:1 polyol 10.85, 4:1 polyol 9.72.

EXAMPLE 7

In a similar manner to example 2, tetrahydropyrimidine, Ic (R═CH₃ CH₂CH₂ --) (100 g) was reacted with 194.8 g of 37% formaldehyde (1/4 molarratio). 154.6 g of viscous product (89.8% of theory) was obtained.

% N:Found 9.90; % N:Calc. 3/1 polyol 10.85, 4/1 polyol 9.72.

EXAMPLE 8

To a 500 ml. three-neck flask equipped with a mechanical stirringthermometer, and reflux condenser was charged 101 g oftetrahydropyrimidine, Ic ##STR18## 162.3 g of 37% formaldehyde, and 100ml of isopropyl alcohol. After 16 hrs. of stirring at room temperaturethe solvent was removed by distillation under reduced pressure. 136.7 gof viscous liquid (84.7% of theory) was obtained.

% N:Found 8.57; % N:Calc. 3/1 polyol 9.59, 4/1 polyol 8.69.

EXAMPLE 9

In a similar manner to example 2, tetrahydropyrimidine, Ie (R₅ +R₆═--(CH₂)₅ --) (20.3 g) treated with 36.8 g of 37% formaldehyde (1/3molar ratio) to yield a viscous product.

Main product, structure found to be as follows: ##STR19## The aboveproduct is the result of a dehydration reaction of the methylol group inthe 5-position under the reaction conditions used.

EXAMPLE 10

In a similar manner to example 2, Ie (20 g) was treated with 16.2 g of37% formaldehyde to yield a viscous product. (1/2 molar ratio).

EXAMPLE 11

In a similar manner to example 2, Ie (20 g) was treated with 8.1 g of37% formaldehyde to yield a viscous product (1/1 molar ratio).

USES

This invention also relates to the inhibition of corrosion, particularlythe corrosion of metals in contact with the acid solutions.

The present invention is especially useful in the acidizing or treatingof earth formations and wells traversed by a bore hole. It may also beused in metal cleaning and pickling baths which generally compriseaqueous solutions of inorganic acids such as sulfuric acid, hydrochloricacid, phosphoric acid and are useful in the cleaning and treatment ofiron, zinc, ferrous alloys, and the like.

If no corrosion inhibitor is present when the aqueous acidic solutioncomes in contact with the metal, excessive metal loss and consumption orloss of acid, and other adverse results will be experienced. There hasbeen a continuing search for corrosion inhibitors which can be usedeffectively in small concentrations and which are economical to produce.The need is also for corrosion inhibitors which are effective at hightemperatures, e.g., 200° F. and above, such as are found in operationsinvolving acidic solutions, particularly oil-well acidizing where higherand higher temperatures are found as the well extends further into theearth.

While the compounds of this invention are of themselves particularlygood acid corrosion inhibitors, optionally they may be blended withacetylenic alcohols, dispersing and solubilizing agents such asethoxylated phenols, alcohols, and fatty acids. They may also be blendedwith such known acid inhibitors as the quinoline or alkyl pyridinequaternary compounds or synergists such as terpene alcohols, formamide,formic acid, alkyl amine, alkylene polyamines, heterocyclic amines, andthe like.

USE IN FLUIDS FOR DRILLING WELLS

This phase of the invention relates to the use of the compounds of thisinvention as corrosion inhibitors in producing an improved drillingfluid useful in drilling oil and gas wells.

Fluids commonly used for the drilling of oil and gas wells are of twogeneral types: water-base drilling fluids comprising, for example, aclay suspended in water, and oil-base drilling fluids comprising, forexample a clay or calcium carbonate suspended in mineral oil.

A third type of drilling fluid which has recently been developed, is oneof oil-in-water or water-in-oil emulsion, for example, emulsions ofmineral oil in water or water in mineral oil formed by means ofemulsifiers such as sulfuric acid; Turkey-red oil; soaps of fatty acids,for example, sodium oleate; emulsoid colloids, for example, starch,sodium alginate, etc. Varying amounts of finely divided clay, silica,calcium carbonate, blown asphalt and other materials may be added tothese emulsions to improve their properties and control their weight.

The compositions of this invention can be employed as a corrosioninhibitor in drilling fluids.

USE IN AIR DRILLING

It has long been conventional practice in drilling deep bore holes tocirculate a drilling mud down through the drill stem and up through thebore hole between the wall of the bore hold and the drill stem for theremoval of chips or cuttings from the bore hole and to provide supportfor the wall of the bore hole. More recently, in the drilling of holesin which wall support provided by drilling mud is not employed, drillinghas been carried out with the use of air for chip removal. Such drillingis not only normally faster than mud drilling but is indispensible inareas where the supply of water is limited or when drilling throughcavernous formations into which the drilling mud flows and becomes lost.

The increasing popularity of air or gas drilling has come about not onlybecause this method of drilling is frequently faster, as noted above,but for the additional reasons that the drill bits last longer, theprovision and handling of water under wide ranges of temperatureconditions is avoided, boring samples are easily observed when they arenot mixed with mud, and there is no loss involved as in the case of muddrilling when drilling through cavernous formations. Furthermore, promptremoval of water entering the hole maintains a dry hole and thelikelihood of wall collapse is thereby reduced.

In a typical air drilling operation there may be provided, for example,an up-flow of air in the bore hole having a velocity of the order of3,000 feet per minute. This flow of air upwardly through the bore hole,which is produced by air pumped downwardly through the drill stem,provides adequate removal of cuttings. The air is delivered to the drillstem at pressure of 20 to 60 lbs. per square inch and for dewatering orfor breaking obstructions, as will be hereinafter described, thepressures may be increased to 180 to 200 lbs. or more per square inch.

Air drilling operations are frequently hampered by the inflow of waterinto the bore hole when the drill bit is penetrating a water bearingstratum or when the bore hole has passed through a water bearing stratumthat has not been cased. Normally, if drilling proceeds uninterruptedlyboth before and during penetration into a water bearing stratum, theflow of air is sufficient to blow the water out of the bore hole alongwith the cuttings and drilling dirt. There are, however, two majorproblems encountered in air drilling when water is entering the borehole. The first problem occurs when there is a small inflow of watersufficient to cause a dampening of the cuttings which, under certainconditions, will then ball-up, clogging and sometimes jamming the drillbit. The second problem is encountered when there is a substantialamount of water remaining in the bottom of the bore hole during drillingcausing a sloughing of the side wall of the bore hole. This lattercondition may arise even though the water entering the bore hole isbeing blown out of the hole as fast as it enters. If there is asubstantial inflow of water or if there is a substantial flow of waterpast a region of the bore hole susceptible to this condition, the waterpassing that region of the bore hole may cause a sloughing of the sidewall.

The addition of foam forming materials to the air flow when air drillingis employed in conjunction with sufficient water to provide foaminggives rise to numerous advantages in drilling operations. The water maybe introduced either through a water bearing stratum being penetrated bythe drill bit or, alternatively, if the hole is dry, water may beintroduced from the surface of the earth through the drill stem inconjunction with the delivery of compressed air and foam formingmaterial through the drill stem to the drill bit. In either case thewater may be said to be existing in the bore hole, and drillingoperations are described in U.S. Pat. No. 3,130,798.

The amount of the composition of the invention to be employed as acorrosion inhibitor can vary widely depending upon particular compounds,the particular system, the amounts of oxygen present, etc. We may employconcentrations of from about 0.5 to 5,000 p.p.m., such as from about 4to 4,000 p.p.m., for example from about 20 to 2,000 p.p.m., butpreferably from about 100 to 1,000 p.p.m. The optimum amount, to bedetermined in each instance, which will depend on function andeconomics, can be lesser or greater than the above amounts under properconditions.

USE IN BRINES

This phase of the invention relates to the prevention of corrosion insystems containing a corrosive aqueous medium, and most particularly insystems containing brines.

More particularly, this invention relates to the prevention of corrosionin the secondary recovery of petroleum by water flooding and in thedisposal of waste water and brine from oil and gas wells. Still moreparticularly, this invention relates to a process of preventingcorrosion in water flooding and in the disposal of waste water and brinefrom oil and gas wells which is characterized by injecting into anunderground formation an aqueous solution containing minor amounts ofcompositions of this invention, in sufficient amounts to prevent thecorrosion of metals employed in such operation. This invention alsorelates to corrosion inhibited brine solutions of these compounds.

When an oil well ceases to flow by the natural pressure in the formationand/or substantial quantities of oil can no longer be obtained by theusual pumping methods, various processes are sometimes used for thetreatment of the oil-bearing formation in order to increase the flow ofthe oil. These processes are usually described as secondary recoveryprocesses. One such process which is used quite frequently is the waterflooding process wherein water is pumped under pressure into what iscalled an "injections well" and oil, along with quantities of water,that have been displaced from the formation, are pumped out of anadjacent well usually referred to as a "producing well." The oil whichis pumped from the producing well is then separated from the water thathas been pumped from the producing well and the water is pumped to astorage reservoir from which it can again be pumped into the injectionwell. Supplementary water from other sources may also be used inconjunction with the produced water. When the storage reservoir is opento the atmosphere and the oil is subject to aeration this type of waterflooding system is referred to herein as an "open water floodingsystem." If the water is recirculated in a closed system withoutsubstantial aeration, the secondary recovery method is referred toherein as a "closed water flooding system."

Because of the corrosive nature of oil field brines, to economicallyproduce oil by water flooding, it is necessary to prevent or reducecorrosion since corrosion increases the cost thereof by making itnecessary to repair and replace such equipment at frequent intervals. Wehave now discovered a method of preventing corrosion in systemscontaining a corrosive aqueous media, and most particularly in systemscontaining brines, which are characterized by employing the compositionsof this invention.

We have also discovered an improved process of protecting from corrosionmetallic equipment employed in secondary oil recovery by water floodingsuch as injection wells, transmission lines, filters, meters, storagetanks, and other metallic implements employed therein and particularlythose containing iron, steel, and ferrous alloys, such process beingcharacterized by employing in water flood operation the compositions ofthis invention.

This phase of the invention then is particularly concerned withpreventing corrosion in a water flooding process characterized by theflooding medium containing an aqueous or an oil field brine solution ofthese compounds.

In many oil fields large volumes of water are produced and must bedisposed of where water flooding operations are not in use or wherewater flooding operations cannot handle the amount of produced water.Most States have laws restricting pollution of streams and land withproduced waters, and oil producers must then find some method ofdisposing of the waste produced salt water. In many instances,therefore, the salt water is disposed of by injecting the water intopermeable low pressure strata below the fresh water level. The formationinto which the water is injected is not the oil producing formation andthis type of disposal is defined as salt water disposal or waste waterdisposal. The problems of corrosion of equipment are analagous to thoseencountered in the secondary recovery operation by water flooding.

The compositions of this invention can also be used in such waterdisposal wells thus providing a simple and economical method of solvingthe corrosion problems encountered in disposing of unwanted water.

Water flood and waste disposal operations are too well known to requirefurther elaboration. In essence, in the present process, the floodingoperation is effected in the conventional manner except that theflooding medium contains a minor amount of the compound of thisinvention, sufficient to prevent corrosion, in concentrations of about10 p.p.m. to 10,000 p.p.m., or more, for example, about 50 to 5,000p.p.m., but preferably about 15 to 1,500 p.p.m. The upper limitingamount of the compounds is determined by economic considerations. Sincethe success of a water flooding operation manifestly depends upon itstotal cost being less than the value of the additional oil recoveredfrom the oil reservoir, it is quite important to use as little aspossible of these compounds consistent with optimum corrosioninhibition. Optimum performance is generally obtained employing about1,000 p.p.m. Since these compounds are themselves inexpensive and areused in low concentrations, they enhance the success of a floodoperation by lowering the cost thereof.

In addition, these compounds are not sensitive to oxygen content of thewater and these are effective corrosion inhibitors in both open waterflooding systems and closed water flooding systems.

While the flooding medium employed in accordance with the presentinvention contains water or oil field brine and the compounds, themedium may also contain other materials. For example, the floodingmedium may also contain other agents such as surface active agents ordetergents which aid in wetting throughout the system and also promotethe desorption of residual oil from the formation, sequestering agentswhich prevent the deposition of calcium and/or magnesium compounds inthe interstices of the formation, bactericides which prevent theformation from becoming plugged through bacterial growth, tracers, etc.Similarly, they may be employed in conjunction with any of the operatingtechniques commonly employed in water flooding and water disposalprocesses, for example five spot flooding, peripheral flooding, etc.,and in conjunction with other secondary recovery methods.

USE IN ACID SYSTEMS

The compounds of this invention can also be employed as corrosioninhibitors for acid systems, for example as illustrated by the picklingof ferrous metals, the treatment of calcareous earth formations, etc.,as described in the following sections.

USE AS PICKLING INHIBITORS

This phase of the invention relates to pickling. More particularly, theinvention is directed to a pickling composition and to a method ofpickling ferrous metal. The term "ferrous metal" as used herein refersto iron, iron alloys and steel.

To prepare ferrous metal sheet, strip, etc. for subsequent processing,it is frequently desirable to remove oxide coating, formed duringmanufacturing, from the surface. The presence of oxide coating, referredto as "scale" is objectionable when the material is to undergosubsequent processing. Thus, for example, oxide scale must be removedand a clean surface provided if satisfactory results are to be obtainedfrom hot rolled sheet and strip in any operation involving deformationof the product. Similarly, steel prepared for drawing must possess aclean surface and removal of the oxide scale therefrom is essentialsince the scale tends to shorten drawing-die life as well as destroy thesurface smoothness of the finished product. Oxide removal from sheet orstrip is also necessary prior to coating operations to permit properalloying or adherence of the coating to the ferrous metal strip orsheet. Prior to cold reduction, it is necessary that the oxide formedduring hot rolling be completely removed to preclude surfaceirregularities and enable uniform reduction of the work.

The chemical process used to remove oxide from metal surfaces isreferred to as "pickling." Typical pickling processes involve the use ofaqueous acid solutions, usually inorganic acids, into which the metalarticle is immersed. The acid solution reacts with the oxides to formwater and a salt of the acid. A common problem in this process is"overpickling" which is a condition resulting when the ferrous metalremains in the pickling solution after the oxide scale is removed fromthe surface and the pickling solution reacts with the ferrous basemetal. An additional difficulty in pickling results from the liberatedhydrogen being absorbed by the base metal and causing hydrogenembrittlement. To overcome the aforementioned problems in pickling, ithas been customary to add corrosion inhibitors to the pickling solution.

The present invention avoids the above described problems in picklingferrous metal articles and provides a pickling composition whichminimizes corrosion, overpickling and hydrogen embrittlement. Thus thepickling inhibitors described herein not only prevent excessivedissolution of the ferrous base metal but effectively limit the amountof hydrogen absorption thereby during pickling. According to theinvention, a pickling composition for ferrous metal is provided whichcomprises a pickling acid such as sulfuric or hydrochloric acid and asmall but effective amount of the compounds of this invention, forexample at least about 5 p.p.m., such as from about 100 to 10,000p.p.m., but preferably from about 3,000 to 7,000 p.p.m.

Ferrous metal articles are pickled by contacting the surface (usually byimmersions in the pickling solution) with a pickling composition asdescribed to remove oxide from their surface with minimum dissolutionand hydrogen embrittlement thereof and then washing the ferrous metal toremove the pickling composition therefrom.

USE IN ACIDIZING EARTH FORMATIONS

The compositions of this invention can also be used as corrosioninhibitors in acidizing media employed in the treatment of deep wells toreverse the production of petroleum or gas therefrom and moreparticularly to an improved method of acidizing a calcareous ormagnesium oilbearing formation.

It is well known that production of petroleum or gas from a limestone,dolomite, or other calcareous-magnesian formation can be stimulated byintroducing an acid into the producing well and forcing it into the oilor gas bearing formation. The treating acid, commonly a mineral acidsuch as HCl, is capable of forming water soluble salts upon contact withthe formation and is effective to increase the permeability thereof andaugment the flow of petroleum to the producing well.

These compounds were tested as HCl Pickle acid corrosion inhibitorsaccording to the following procedure:

HCL Pickle Acid Test Procedure

I. Equipment

Oil Bath--capable of maintaining 200° F.;

Analytical Balance;

300 ml beakers;

7/8×31/4×1/6 1020 mild steel coupons;

HCl pickle Acid;

Watch glasses

HCl Pickle Acid

To 500 ml of tap water, add 135 ml of reagent grade (37%) HCl. Thendissolve 240 g FeCl₂ -4H₂ O. Dilute to 1 liter with tap water. (This isabout 5% HCl and 7% Fe).

II. Procedure

Preheat oil bath to 190° F. ;

Put 200 ml of HCl Pickle Acid in a 300 ml beaker and then place in oilbath. Leave acid in oil bath for one (1) hour so that the acid is at thecorrect temperature.

Add chemical to be tested. The standard concentration used is 0.25% (0.5ml of inhibitor/200 ml acid); however, this can be changed at thediscretion of the tester.

Clean the coupons by immersing briefly (5-10 seconds) in 15% HCl, thenin hot water, then in hot acetone and air dry.

Weigh coupons;

Place coupons in test beakers at 30 second intervals. Let corrode forexactly one (1) hour.

Note test details--foaming, gas evolution, etc.

Remove coupons at 30 second intervals in original sequence. Immediatelyon removal from test beaker, wash coupon in hot water to remove theacid, then in hot acetone, then air dry. (The thirty (30) secondinterval should allow plenty of time for this).

Reweigh coupons. ##EQU1##

Typical results are presented in the following table.

    ______________________________________                                        0.25% Concentration of Inhibitor                                              Inhibitor    % Protection                                                     ______________________________________                                        Ex. 3        94.3                                                             Ex. 4        94.0                                                             Ex. 5        93.3                                                             ______________________________________                                    

We claim:
 1. Methylol derivatives of 2,3,4,5-tetrahydropyrimidines wherethere is a methylol substitution at two or more of the followingpositions:(1) the ring-N at the 3 position; (2) the ring carbon at the 5position; and (3) 1 or 2 hydrogens of the α-methyl group at the 6position.
 2. The composition of claim 1 where the2,3,4,5-tetrahydropyrimidines prior to methylolation have the formula##STR20## where the R's, which may be same or different, are hydrogen ora substituted group.
 3. The composition of claim 2 where the R's arehydrogen or hydrocarbon group.
 4. The composition of claim 3 where theR's are hydrogen or alkyl.
 5. The composition of claim 4 where the alkylis methyl.
 6. The composition of claim 5 where the tetrahydropyrimidineprior to methylol substitution has the formula ##STR21##
 7. Thecomposition of claim 5 having the formula ##STR22##
 8. Methylolderivatives of 2,3,4,5-tetrahydropyrimidines where there is a methylolsubstitution at the following positions:(1) the ring-N of the 3position; and (2) the ring carbon at the 5 position.